The present invention is designed for use in a well environment. A hole is drilled to the depth of a water or hydrocarbon bearing strata and a casing lowered into the well bore. The casing is cemented into place within the well bore using conventional cementing techniques. A perforating gun of the type generally known in the industry is lowered into the casing to the depth of the strata and is discharged to create a passageway through the casing and cement into the strata. Water or hydrocarbons flow into the casing through the perforations in the cement and the casing. The water or hydrocarbons will usually carry particulate matter with it as it enters the casing. In order to screen out the particulate matter, a tubing "screen" and a well seal are mounted on the end of a pipe string and lowered into the casing to the depth of the strata.
The well is generally flushed to remove contaminates such as drilling fluids or cuttings from the well bore. The well may be flushed by running a flush pipe through the drill pipe and into the tubing screen and forcing running water or compressed air through the pipe. The drilling fluid and other contaminates are forced to the surface by the water or air via the annulus between the drill pipe and the inner wall of the casing. Upon completion of the flushing operations, the annulus to the surface is closed off by setting the well seal. The well seal is set and the pipe string removed, leaving the tubing screen and packer in the well. A tool to activate the well seal is lowered into the well at the end of a pipe string. This process of removing the pipe string or re-inserting the pipe string is known as "tripping." The tripping of a well can require several hours and results in increased costs during drilling operations. Upon activation of the well seal, the pipe string is tripped out of the hole and a production tubing string is lowered into the well to mate with the tubing screen. As with shallower wells, the water may reach the surface as a result of hydrological pressure or may be assisted by pump means. The seal operates to assure all water reaching the surface passes through the tubing screen by sealing off the annulus to the surface.
There are a number of different methods known for sealing the annulus. One of the most common is known as the "lead seal" similar to those described in U.S. Pat. Nos. 411,886 and 1,336,738, and in a publication by Western Well Screen Co.. This type of seal includes a deformable soft metal collar which is threaded onto the end of the tubing screen. The tubing screen and the seal are then lowered into the casing at the end of a pipe string. The well is then flushed in the manner described above. The pipe string is then retrieved leaving the tubing screen and seal in the casing at the depth of the water bearing strata. A tapered sealing iron is then lowered at the end of a pipe string and inserted into the seal. The weight of the pipe string deforms the soft metal collar such that the collar comes into contact with the inner wall of the casing, thus sealing the annulus. However, there are a number of disadvantages to this type of seal. Primary among them is the danger of potable water metal contamination from the soft metal seal which is often made of lead. Second, the deformed metal seal often fails to completely seal the annulus, permitting unfiltered water to rise to the surface via the annulus, carrying particulate matter with it. Lastly, this type of seal requires that the flaring tool be lowered on the end of a pipe string requiring additional trips in the well and resulting in additional cost.
A variation on this type of seal is a non-lead seal as disclosed in a publication by the BP Seal Co. of Houston, Tex. The publication discloses a wire screen encased in an elastomeric material. As with lead seals, the seal and tubing screen are lowered in the well at the end of a pipe string. The screen and seal are released and the pipe string retracted. A flaring tool is then lowered at the end of a pipe string to deform the seal such that the elastomeric material comes into contact with the inner wall of the casing sealing the annulus. Unlike the lead seal, the seal is achieved between the elastomeric material and the casing wall. The screen within the elastomeric material is deformed to hold the elastomeric material in place. However, like the lead seal, this type of seal requires an additional trip down well with a flaring tool.
Another known means of sealing the well annulus includes the use of deformable resilient skirts which seal against the inside wall of the casing. These seals are generally activated by a tool which is lowered into the well bore to activate the seal following flushing operations. This type of seal also requires the tripping of a pipe string to activate the well seal, thus increasing the time and cost required to complete the well.
The above prior devices required that the tubing screen be lowered on a pipe string. A pipe string carrying a tool to actuate the well seal was also required in the above devices. Finally, a production string was lowered and connected to the tubing screen to bring the well into production. It will be appreciated that the time and effort involved in making the multiple "trips" into the well could greatly increase the cost and time required to bring a water well into production.
Yet another method for sealing the annulus in a well bore is disclosed in U.S. patent application No. 348,207, filed May 5, 1989, now U.S. Pat. No. 4,930,577. The inventive entity and the owner of application Ser. No. 348,207 are the same entity and owner in this application. Application Ser. No. 348,207 discloses an elastomeric sealing member which is sealed against a well casing by split rings which expand from a compressed position upon the release of a tubing screen and seal body from a drill pipe. Thus, application Ser. No. 348,207 discloses a non-metallic sealing member which may be activated upon installation without the requirement of an additional trip to activate the seal. However, the hydrostatic forces in the well bore would tend to move the sealing member out of contact with the casing.